Adhesives form a large part of daily activity for everyone, whether in the form of tape used to close a package or secure items together, bandages, envelopes, notepads, diaper tabs or any one of many other products in common use. The key requirements for adhesives are that they should have suitable cohesive and adhesive properties at end use conditions and during application, whether by solvent or bulk casting. Usually these adhesives are prepared from a mixture of resin, copolymer and a plasticizer to soften the adhesive and enhance tack.
Adhesives prepared from blends incorporating these polymers have very good adhesive and strength properties at room temperature and can be processed by conventional melt coating and extrusion techniques because of their good flow characteristics. However, when copolymers are mixed with tackifying resins in order to form adhesives, many requirements and factors are important such as the ease with which the resin is blended with the copolymer and the control of the tack as well as the long term properties of the adhesive. Further, the adhesives industry has increased the demand for low softening point resins and market requirements dictate the desirability of resins which are not only liquid, i.e., softening point about 40.degree. C. or less, but that are light in color, even a Gardner color of less than about 3. However, a resin would be considered to be sufficiently light in color for some applications with a Gardner color of 6 or even 7.
Many attempts have been made to prepare resins having these properties for use in the blending with copolymers to form adhesives, but all have fallen short of the mark in one respect or another.
Other attempts have been made to prepare light color, low softening point aliphatic resins including, for example, the disclosure of U.S. Pat. Nos. 3,813,357; 3,692,756; 3,661,870; 3,804,788; 3,853,826; 3,872,064; 4,098,983; 4,038,346; 4,153,771; and 4,189,547.
Petroleum hydrocarbon resins may be obtained by polymerizing, using a Friedel-Crafts catalyst, a petroleum resin feed comprising C.sub.5 and C.sub.6 olefins and diolefins obtained from the cracking of petroleum feedstock and usually subjected to thermal soaking at about 100.degree. to 150.degree. C., a branched chain reactive aliphatic olefin chain transfer agent, and optionally a C.sub.8 to C.sub.10 vinyl aromatic compound. The reactive olefin transfer agents are feed additives which in part control the resin molecular weight and narrow the resin molecular weight distribution.
Most aliphatic resins do not provide desired adhesive properties with many copolymers. Other components such as a naphthenic oil are required to impart the tack or other requisite adhesive properties to the adhesive composition. The presence of oil itself can cause detrimental adhesive performance. The low color liquid resins of the present invention solve these problems of the prior art.
Most of the patents mentioned above also relate to the preparation of aliphatic or liquid resins using various feedstocks but preparing the resin by boron trifluoride catalyzed polymerization. It is well established that polymerization with BF.sub.3 results in a substantially different polymer than that which is obtained by aluminum chloride Freidel-Crafts polymerization. U.S. Pat. No. 3,853,826 at column B 1, lines 32-36 presents a brief discussion of the structural differences between BF.sub.3 and aluminum chloride catalyzed resins. U.S. Pat. No. 4,098,983 discloses that the BF.sub.3 polymerization of a piperylene/2-methylbutene feed provides a low softening point resin having a high viscosity. In the same disclosure at column 4, Examples 1 and 2 teach that a similar polymerization with aluminum chloride results in high softening point resins, contrary to the present invention.
U.S. Pat. No. 3,692,756 discloses the production of liquid resins and hard resins from blends of C.sub.4 and C.sub.5 olefins and diolefins with aluminum chloride catalysts. This reference teaches the requirement of the presence of a significant portion of butadiene to obtain a liquid resin. In Examples 2 and 5 using low levels of butadiene, a high softening point resin is obtained.
U.S. Pat. No. 3,661,870 describes the production of liquid resins derived from butadiene and chain transfer agents with aluminum chloride as catalyst. While piperylene is a possible low level additive, butadiene is required in significant amount.